Virologic studies for this program will be performed at two different sites. 1.) Quantitation of HIV-RNA by the ultra sensitive Roche RT-PCR Amplicor assay and genotyping for drug resistance will be done in our high through-put Bellevue Hospital laboratory. Measurements of HIV by real time PCR for rapid diagnosis of individuals at the earliest stages of acute infection, and heteroduplex gel tracking assays to monitor viral evolution will be performed in the Borkowsky CFAR laboratory at Bellevue Hospital. 2.) Total genomic sequencing of HIV isolates from multiple time points in up to 15 patients per year, and the "detuned" ELISA assays will be performed. All projects in this program will correlate their immunological data with the viral load measurements and HIV-genomic sequences provided by this core. Studies of the evolution of CD4 responses will be compared with the evolution of the subjects' HIV as documented by heteroduplex analyses, by sequencing, and by mapping changes in epitopes of the viruses with the peptides recognized by the CD4 cells.